Nutritionists are often asked to walk the fine line of maximizing milk production per cow without compromising animal health.

Preventing subacute ruminal acidosis (SARA) can be a real challenge. Some level of SARA is inevitable even in the best managed high producing herds because of high intakes. Subacute acidosis is caused by the rapid accumulation of volatile fatty acids (VFA) in the rumen (acetate, propionate, and butyrate) which results in periods of low pH and this situation is exacerbated by high dry matter intake.

Researchers from the University of Alberta presented a paper at the 2009 Tri-State Dairy Nutrition Conference that discussed the latest developments in our understanding of ruminal acidosis. They found that there is a great deal of variability in the susceptibility of individual cows to SARA. Some cows are much more likely to exhibit symptoms of SARA than others, presumably due to differences in intake level, eating rate, salivation, feed sorting and inherent rumen physiological variation. For these reasons, it’s almost impossible to totally eliminate SARA in a high producing herd when rations are balanced for the average cow.

They stated that the key to maintaining rumen health is adaptation and stability by avoiding rapid dietary changes. Fresh cows are especially at risk because of the abrupt change to higher fermentable carbohydrate diets to support high production after calving. Variable intake due to heat stress adds to the challenge. Transition programs need to be designed so that both the ruminal epithelium and the rumen microbes adapt to dietary changes. Rumen papillae shorten during the dry period due to low intake of fermentable carbohydrates and then lengthen as the cow is fed more grain in the close up period. It can take up to 8 weeks of adaptation for maximum papillae growth. The ruminal epithelium absorbs VFA and prevents them from accumulating in the rumen. But the ruminal epithelium regresses as intake is depressed just prior to calving. The functionality of the epithelium may be more important than the papillae surface area to help clear the rumen of accumulating VFA. So strategies to minimize feed intake depression just prior to calving will help reduce the severity of acidosis after calving.

Other important considerations include controlling the rate of starch digestion by gradual changes in grain intake, replacing a portion of the grain with non-forage fiber sources such as beet pulp, soyhulls, citrus pulp and gluten feed and providing sufficient physically effective fiber from good quality forages. Additives such as sodium bicarbonate, potassium carbonate, yeast and Rumensin can also help modify the rumen environment to help reduce SARA.

--Rick Lundquist is an independent nutrition and management consultant based in Duluth, Minn. You can contact him at siestadog@aol.com.

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